The present invention relates to the use of a prepreg for the production of a composite and to an active orthodontic method of treatment. The invention further relates to an active orthodontic appliance comprising an arch wire consisting essentially of a fiber-reinforced composite comprising at least one fiber and a matrix, as well as to a process for manufacturing an active orthodontic appliance.
In active orthodontic treatment teeth are rearranged by removable or fixed orthodontic appliances in order to achieve better occlusal stability, function as well as appearance. Orthodontic treatment is based on the principle that if prolonged pressure is applied to a tooth, tooth movement will occur as the bone around the tooth remodels. Tooth movement can be bodily movement, tipping, root uprighting, rotation, extrusion or intrusion.
The state-of-the-art methods to move teeth are based on using fixed orthodontic appliances. These appliances comprise metallic or ceramic brackets adhered to the teeth and a metal arch wire (e.g. nickel-titanium alloy), which is bent in such a way that it transfers a desired force to the teeth. Shortcomings of the state-of-the-art method are e.g. structural complicity of the appliances which can cause oral hygiene problems resulting in decay, and poor appearance of the appliance. To overcome the appearance problem, tooth colored ceramic brackets and fiber-reinforced composite brackets (Adam et al, U.S. Pat. No. 5,318,440) have been introduced. However, despite the development of the bracket materials, one problem still occurs, i.e. the quite frequent loosening of the brackets from the tooth surface. The problem is due to the fact that high strength metals and ceramics (such as titanium alloys and zirconium oxides) are difficult to adhere to the tooth surface in clinical conditions.
Recently, fiber-reinforced composites (FRC) have been introduced for dental use. One application of FRCs is to replace metal wires used as an orthodontic arch wires. This has been described by Kusy and Kennedy (U.S. Pat. No. 5,987,376), Goldberg and Burstone (U.S. Pat. No. 4,717,341) and Kobayashi et al (U.S. Pat. No. 5,759,029). The system uses continuous unidirectional glass fiber wire as a translucent, i.e. aesthetic, arch wire in combination with traditional brackets. In all of these inventions, a cured FRC arch wire, i.e. FRC arch wire with a finally polymerized matrix, and brackets is used.
The object of the invention is to provide an active orthodontic appliance that does not have the above-mentioned drawbacks. It is thus an object of the invention to provide an appliance having a simple, reliable and aesthetic structure, which allows the maintenance of good oral hygiene.
Another object of the invention is to provide an active orthodontic appliance that may be attached to teeth without using brackets. An object of the invention is also to provide a process for manufacturing said appliance. Yet another object of the invention is to provide a novel use for a prepreg as well as to provide a new method of active orthodontic treatment.
The invention relates to the aspects defined in the annexed claims.
The invention relates to the use of a prepreg comprising at least one fiber and a matrix to be cured during application, for the production of a fiber-reinforced composite, for active orthodontic therapy.
The invention further relates to an active orthodontic appliance consisting essentially of an arch wire in at least one part, directly contactable with teeth and consisting essentially of a fiber-reinforced composite comprising at least one fiber and a matrix, said arch wire comprising a loop directly contactable with a tooth or teeth to be moved by the appliance.
The invention also relates to a process for manufacturing an active orthodontic appliance comprising the steps of:
a) shaping a first portion of a prepreg consisting of a composition comprising at least one fiber and a matrix in its non-cured form, to the shape of the tooth or teeth to be used as support for the appliance,
b) shaping a second portion of the prepreg to the shape of the tooth or teeth to be obtained by the appliance,
c) curing said prepreg to obtain a composite, and
d) forcing the second portion of the composite obtained to the original shape of the tooth or teeth to be moved by the appliance.
The invention still relates to an active orthodontic method of treatment comprising the steps of
a) shaping a first portion of a prepreg consisting of a composition comprising at least one fiber and a matrix in its non-cured form, to the shape of the tooth or teeth to be used as support,
b) shaping a second portion of the prepreg to the shape at the end of the orthodontic treatment,
c) curing said prepreg to obtain a composite,
d) forcing said second portion of the composite to the shape at the beginning of the orthodontic treatment to obtain an orthodontic appliance, and
e) contacting said appliance to said teeth for the duration of said treatment.
In this application, by curing it is meant polymerization and/or crosslinking. By matrix, it is understood the continuous phase of the composition and by matrix in its non-cured form it is meant a matrix that is in its deformable state but that can be cured, i.e. hardened, to a non-deformable state. The matrix in its non-cured form may already comprise some long chains but it is essentially not yet polymerized. By prepreg, it is meant a semi-manufactured product, that is, a product that is non or partly polymerized yet still deformable. The polymerization of a prepreg leads to a composite. The words xe2x80x9ccompositexe2x80x9d and xe2x80x9ccured prepregxe2x80x9d may be used interchangeably.
The invention relates to the use of a prepreg comprising at least one fiber and a matrix to be cured during application, for the production of a fiber-reinforced composite, for active orthodontic therapy.
By application, it is meant the manufacturing of an active orthodontic appliance, that is, the operation performed by a dentist or a dental technician to provide an appliance suitable for specific needs of the patient, starting from a prepreg. The manufacturing comprises also the assembly of the device from semi-finished products and the curing to obtain said device.
The main difference of the present invention with the prior art is that in the present invention, the prepreg is cured to composite during the manufacturing of the appliance itself, whereas in the prior art, the prepreg is first cured to form a composite and thereafter the appliance is manufactured from said composite.
According to an embodiment of the invention, said composite is for direct contact to the teeth involved in said active orthodontic therapy. The composite of the invention may therefore be used in an orthodontic appliance without brackets, thus achieving one of the objects of the invention. The appliance may be attached to the teeth by means of dental adhesive, for example.
The invention further relates to an active orthodontic appliance consisting essentially of an arch wire in at least one part, directly contactable with teeth and consisting essentially of a fiber-reinforced composite comprising at least one fiber and a matrix, said arch wire comprising a loop directly contactable with a tooth or teeth to be moved by the appliance.
The appliance according to the invention thus has a simple and reliable structure allowing the maintenance of good oral hygiene. In addition, the appliance according to the invention is aesthetic since it does not require brackets and it is possible to make the appliance of the same color as the patient""s teeth, so that the appliance is almost invisible. A further advantage of the appliance according to the invention is the increased convenience and comfort to the patient, due to the lack of brackets.
In summary, it can be said that the activation of the present inventive arch wire to move the teeth is obtained by polymerizing the fully impregnated prepreg""s matrix to the desired form before adhering the inventive arch wire to the tooth enamel surface. After polymerization by e.g. light or laser, the arch wire is bent and attached to the tooth surface by means of dental adhesives, for example. It is also possible to attach the appliance to the teeth only once the whole appliance is ready. The bending causes internal stresses to the inventive arch wire, which are going to move the tooth to the desired location, as the arch wire tends to return to its original shape.
According to an embodiment of the invention, the arch wire is in one part and according to another embodiment the arch wire is in at least two parts. When the arch wire is in one part, it forms a loop that is either attached to the tooth or teeth to be moved or passed over it, in which case it does not necessarily need to be attached, the contact together with the stress is enough to keep it in place during the treatment. The arch wire may also be in two or more parts. In this case, the first part of the arch wire is formed to the position desired at the end of the treatment. The tooth or teeth to be moved is/are then connected to the first part of the arch wire by a second (and optionally further) part(s) of the arch wire. More complicated misalignment of teeth may be corrected with this kind of appliance than when the arch wire is in one part. The first and further parts of the arch wire are thus in an angle with respect to each other. This embodiment will be further illustrated in the Figures below.
According to an embodiment of the invention, the orthodontic appliance is attached to each individual tooth by means of a dental adhesive.
The fiber or fibers used in the composition may be any fiber known per se and a person skilled in the art will be able to readily assess which fiber is the most suitable for the intended application. The choice of the fibers depends on the force needed for the movement of the teeth and the esthetic demands. Some examples of suitable fibers are glass fibers (S and E), silica fibers, quartz fibers, carbon fibers, ceramic fibers, polyolefin fibers, fibers prepared from copolymers of olefins, aramide fibers, polyester fibers, polyamide fibers, polyacrylic fibers. One composition may comprise one or more different types of fibers. The proportion of the fibers in the resin matrix should be preferably chosen so to give desired flexural properties to the appliance, i.e. tooth moving force after being activated after light polymerization in situ or chair-side and bending. The suitable volume fractions of the fibers vary between 10 and 70%.
The composition may comprise one, two, three, four, five, six or more continuous or semi-continuous fibers and/or staple, i.e. short, fibers. Preferably, the length of the fibers is at least 5 mm. By semi-continuous fibers it is meant that the fibers are shorter than the largest dimension of the resulting appliance and that at least two separate groups of fibers exist in the direction of said largest dimension. These at least two groups may overlap. The suitable diameter of the fiber(s) will also be evident to a person skilled in the art. Furthermore, the fibers may be used individually or in bundles. The fibers may also be in several bundles. The most appropriate configuration of the fibers will be obvious to a person skilled in the art in view of the result to achieve. Some examples of the configurations are given below in connection with the drawings.
According to a preferred embodiment of the invention, the fibers or fiber bundles are at a first distance from each other on the tooth enamel surface and at a second distance from each other between the teeth and that said second distance is essentially smaller than said first distance. In other words, the fibers or fiber bundles are spread on the tooth surface and in tight groups between the teeth, i.e. between the points of attachment to the teeth. The tight group form after having been polymerized to the desired location is the active part of the appliance forcing the tooth to be moved.
According to yet another embodiment of the invention, the orientation of the fibers of said prepreg are continuous unidirectional, bi-directional, tri-directional or any combination thereof. Generally, continuous unidirectional fibers are preferred due the high strength and high modulus properties in one direction (anisotropic materials). However, in applications where for example torque forces are needed, a combination of unidirectional fibers and bi-directional fibers result in more suitable tooth torque forces. This may be achieved by the configuration mentioned above in relation with the arch wire in two or more parts. In general, a person skilled in the art will be able to define the proper assembly of fiber groups in order to obtain the desired force in proper direction and amount.
The matrix used in the composition may be made of known monomer, dendrimer, oligomer or polymer and a person skilled in the art will be able to readily assess which material is the most suitable for the intended application. Some examples of suitable the matrix in its non-cured form are mono-, di-, tri- or multifunctional acrylates or methacrylates such as methyl methacrylate, ethyleneglycol dimethacrylate, bis-hydroxy-methacryloxyphenyl propane, triethyleneglycol dimethacrylate, polymethyl methacrylate, urethan dimethacrylate, as well as epoxies, esters, acrylics, sulfones, carbonates, dendrimers and combinations thereof. Dendrimers having 5 to 35 functional groups such as methacrylate or acrylate groups are preferred. Multifunctionality forms highly cross-linked matrix and decreases the creep of the polymer in the long-term use of the present appliance.
Examples of suitable dendrimers are given for example in U.S. Pat. No. 5,834,118 that is incorporated herein by reference. Dendrimers may particularly be startburst or hyperbranched methacrylated polyesters.
The curing in the invention is performed by a known curing process suitable for the selected matrix. The curing may be induced for example by electromagnetic radiation independently selected from the group consisting of visible light, ultra-violet light, blue light and laser irradiation. The wording xe2x80x9cindependently selectedxe2x80x9d means that different radiations may be used in different steps of the method. According to another embodiment, said matrix is autopolymerizable and the curing is induced by applying an activator on the prepreg. It is also possible to use matrixes that are stored in low temperatures (under room temperature or below 0xc2x0 C.) after manufacturing and that autopolymerize once the temperature is increased to room temperature. The preferable polymerization initiation is obtained by radiation with blue light or by laser by help of initiators and activators for the free radical polymerization.
It is obvious to a person skilled in the art that the combination of fiber(s) and matrix need to be chosen so that the mechanical properties of the resulting appliance are suitable for intended use. By mechanical properties it is meant here for example the flexural properties, creep properties and tensile strength properties.
The invention also relates to a process for manufacturing an active orthodontic appliance comprising the steps of:
a) shaping a first portion of a prepreg consisting of a composition comprising at least one fiber and a matrix in its non-cured form, to the shape of the tooth or teeth to be used as support for the appliance,
b) shaping a second portion of the prepreg to the shape of the tooth or teeth to be obtained by the appliance,
c) curing said prepreg to obtain a composite, and
d) forcing the second portion of the composite obtained to the original shape of the tooth or teeth to be moved by the appliance.
According to the an embodiment of the invention, the process further comprises a second curing step e) after the step a) and before the step b) in which step said first portion of the prepreg is cured to obtain a first portion of a composite. The prepreg may thus be cured in one or two parts. It is obvious to a person skilled in the art that the prepreg may also be cured in more that two distinct steps of process.
The appliance may be manufactured either outside the mouth, i.e. shaped on a model and then attached to the teeth, or in situ, i.e. in the mouth of the patient.
The fibers and matrix used in the composition as well as the curing processes have been discussed above in connection with the appliance and the use of the prepreg.
The invention still relates to an active orthodontic method of treatment comprising the steps of:
a) shaping a first portion of a prepreg consisting of a composition comprising at least one fiber and a matrix in its non-cured form, to the shape of the tooth or teeth to be used as support,
b) shaping a second portion of the prepreg to the shape at the end of the orthodontic treatment,
c) curing said prepreg to obtain a composite,
d) forcing said second portion of the composite to the shape at the beginning of the orthodontic treatment to obtain an orthodontic appliance, and
e) contacting said appliance to said teeth for the duration of said treatment.
According to an embodiment of the inventive method of treatment, it further comprises a step f) between steps a) and b) consisting of curing said first portion of the prepreg to obtain a first portion of a composite.
According to another embodiment of the invention, said method further comprises a step g) between steps b) and c) consisting of attaching said first portion of the composite to the tooth or teeth.
According to another embodiment of the invention, said composite is directly in contact with said tooth or teeth. The composite may thus be either directly attached to said tooth or teeth or it may form a loop that is passed over the tooth or teeth, thereby not requiring the attachment of the composite.
According to yet further embodiments of the invention, the composite is in steps f) and/or g) attached to each individual tooth by means of a dental adhesive.
The fibers and matrix used in the composition as well as the curing processes have been discussed above in connection with the appliance and the use of the prepreg.